U.S. patent number 7,434,551 [Application Number 11/771,823] was granted by the patent office on 2008-10-14 for constant temperature internal combustion engine and method.
This patent grant is currently assigned to Zajac Optimum Output Motors, Inc.. Invention is credited to James Peter Chand, John Zajac.
United States Patent |
7,434,551 |
Zajac , et al. |
October 14, 2008 |
Constant temperature internal combustion engine and method
Abstract
Internal combustion engine and method with compression and
expansion chambers of variable volume, a combustion chamber, a
variable intake valve for controlling air intake to the compression
chamber, a variable outlet valve for controlling communication
between the compression chamber and the combustion chamber, means
for introducing fuel into the combustion chamber to form a mixture
of fuel and air which burns and expands in the combustion chamber,
a variable inlet valve for controlling communication between the
combustion chamber and the expansion chamber, a variable exhaust
valve for controlling exhaust flow from the expansion chamber,
means for monitoring temperature and pressure conditions, and a
computer responsive to the temperature and pressure conditions for
controlling opening and closing of the valves and introduction of
fuel into to the combustion chamber to optimize engine efficiency
over a wide range of engine load conditions. In some disclosed
embodiments, the relative volumes of the compression and expansion
chambers and the timing of the valves are such that the pressure in
the combustion chamber remains substantially constant throughout
the operating cycle of the engine, and exhaust pressures are very
close to atmospheric pressure regardless of the load on the engine.
In others, the temperature within the combustion chamber is
maintained at a substantially constant level throughout the
operating range of the engine, and the power produced by the engine
is determined by the amount of air passing through the engine. The
engine runs so quietly and burns so cleanly that in some
applications it may not require a muffler and/or a catalytic
converter.
Inventors: |
Zajac; John (San Jose, CA),
Chand; James Peter (San Jose, CA) |
Assignee: |
Zajac Optimum Output Motors,
Inc. (San Jose, CA)
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Family
ID: |
38895404 |
Appl.
No.: |
11/771,823 |
Filed: |
June 29, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070289562 A1 |
Dec 20, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11372751 |
Mar 9, 2006 |
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60806294 |
Jun 30, 2006 |
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Current U.S.
Class: |
123/70R;
60/39.6 |
Current CPC
Class: |
F02B
41/06 (20130101); F02B 41/02 (20130101); Y02T
10/42 (20130101); Y02T 10/40 (20130101) |
Current International
Class: |
F02B
25/00 (20060101); F02C 5/00 (20060101) |
Field of
Search: |
;60/39.6,39.63
;123/68,70R,71R,72 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3242431 |
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May 1984 |
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DE |
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8400997 |
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Mar 1984 |
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WO |
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Other References
Wikipedia Contributors, Brayton cycle, Publication Date: Unknown,
http://en.wikipedia.org/w/index.php?title=Brayton.sub.--cycle&oldid=81660-
788, Wikipedia, The Free Encyclopedia. cited by other.
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Primary Examiner: Kamen; Noah
Attorney, Agent or Firm: Wright; Edward S.
Parent Case Text
RELATED APPLICATIONS
Continuation-in-part of Serial No. 11/372,751, Filed Mar. 9,
2006;
Provisional Application Ser. No. 60/806,294, filed Jun. 30, 2006,
the priority of which is claimed.
Claims
The invention claimed is:
1. An internal combustion engine, comprising: a compression chamber
of variable volume for compressing air taken into the engine, a
combustion chamber for receiving compressed air from the
compression chamber, means for introducing fuel into the combustion
chamber to mix with air from the compression chamber and form a
mixture which burns and expands, an expansion chamber having an
output member which is driven by expanding gas from the combustion
chamber, means for maintaining the temperature within the
combustion chamber at a substantially constant level throughout the
operating range of the engine, and means for controlling the amount
of air passing through the engine to determine the power produced
by the engine.
2. The engine of claim 1 including means for maintaining the
temperature in the combustion chamber at a temperature between
1400.degree. K. and 1800.degree. K.
3. The engine of claim 1 including means for maintaining the
temperature in the combustion chamber at a temperature between
1400.degree. K. and 2000.degree. K.
4. The engine of claim 1 including means for monitoring pressure in
the combustion chamber and adjusting the flow of expanding gas from
the combustion chamber to the expansion chamber to maintain the
pressure in the combustion chamber at a substantially constant
level.
5. The engine of claim 1 including means for boosting the pressure
of the air to a level above atmospheric pressure before the air is
taken into the engine.
6. The engine of claim 1 including means for controlling exhaust
from the engine such that the exhaust is discharged at or near
atmospheric pressure.
7. The engine of claim 1 wherein the compression chamber and the
expansion chamber are cylinders with reciprocating pistons
connected together by a crankshaft.
8. A method of operating an internal combustion engine, the steps
of: introducing air into a compression chamber, compressing air in
the compression chamber, delivering compressed air from the
compression chamber to a combustion chamber, introducing fuel into
the combustion chamber to mix with the air from the compression
chamber and form a mixture which burns and expands, expanding gas
from the combustion chamber in an expansion expansion chamber
having an output member which is driven by expanding gas,
maintaining the temperature within the combustion chamber at a
substantially constant level throughout the operating range of the
engine, and controlling the amount of air passing through the
engine to determine the power produced by the engine.
9. The method of claim 8 wherein the temperature in the combustion
chamber is maintained at a substantially constant temperature
between 1400.degree. K. and 1800.degree. K.
10. The method of claim 8 wherein the temperature in the combustion
chamber is maintained at a substantially constant temperature
between 1400.degree. K. and 2000.degree. K.
11. The method of claim 8 including the steps of monitoring
pressure in the combustion chamber and adjusting the flow of
expanding gas from the combustion chamber to the expansion chamber
to maintain the pressure in the combustion chamber at a
substantially constant level.
12. The method of claim 8 including the step of boosting the
pressure of the air to a level above atmospheric pressure before
the air is introduced into the compression chamber.
13. The method of claim 8 wherein exhaust is discharged from the
expansion chamber at or near atmospheric pressure.
14. The method of claim 8 wherein the expanding gas drives a
reciprocating piston in the expansion chamber.
15. An internal combustion engine, comprising: compression and
expansion chambers of variable volume, a combustion chamber, an
intake valve for controlling air intake to the compression chamber,
an outlet valve for controlling air flow from the compression
chamber to the combustion chamber, an inlet valve for controlling
communication between the combustion chamber and the expansion
chamber, an exhaust valve for controlling exhaust flow from the
expansion chamber, means for introducing fuel into the combustion
chamber to mix with air from the compression chamber and form a
mixture which burns and expands, means for controlling operation of
the intake valve to control the amount of air passing through the
engine and, hence, the amount of power produced by the engine,
means for monitoring temperature in the combustion chamber, and
means responsive to the temperature in the combustion chamber for
controlling the amount of fuel introduced into the combustion
chamber and burned with the air to maintain the temperature in the
combustion chamber at a substantially constant level throughout the
operating range of the engine.
16. The engine of claim 15 including means for monitoring pressure
in the combustion chamber and controlling the inlet valve to
maintain a desired level of pressure in the combustion chamber.
17. The engine of claim 15 including means for increasing the power
produced by the engine by opening the intake valve for a longer
period of time to allow more air to be taken into the compression
chamber, and means for injecting more fuel into the combustion
chamber to maintain the temperature of the burning gas at the
substantially constant level even though more air is taken into the
compression chamber and delivered to the combustion chamber.
18. The engine of claim 15 including means for boosting the
pressure of air supplied to the compression chamber to a level
above atmospheric pressure.
19. The engine of claim 15 including means for advancing the
opening of the outlet valve to maintain a desired compression ratio
in the compression chamber when more air is taken into the
compression chamber.
20. The engine of claim 15 including means for delaying the closing
of the inlet valve to allow additional gas to pass from the
combustion chamber to the expansion chamber.
21. The engine of claim 15 including means for controlling the
opening of the exhaust valve to allow pressure in the expansion
chamber to reach a level at or near atmospheric pressure before the
exhaust valve opens.
22. The engine of claim 15 wherein the compression chamber and the
expansion chamber are cylinders with reciprocating pistons
connected together by a crankshaft.
23. A method of operating an internal combustion engine having
compression and expansion chambers of variable volume, a combustion
chamber, an intake valve for controlling air intake to the
compression chamber, an outlet valve for controlling air flow from
the compression chamber to the combustion chamber, an inlet valve
for controlling communication between the combustion chamber and
the expansion chamber, and an exhaust valve for controlling exhaust
flow from the expansion chamber, the steps of: introducing air into
the compression chamber, compressing air in the compression
chamber, delivering compressed air from the compression chamber to
the combustion chamber, introducing fuel into the combustion
chamber to mix with air from the compression chamber and form a
mixture which burns and expands, controlling the amount of air
passing through the engine and the amount of power produced by the
engine by operation of the intake valve, monitoring temperature in
the combustion chamber, and controlling the amount of fuel
introduced into the combustion chamber and burned with the air to
maintain the temperature in the combustion chamber at a
substantially constant level throughout the operating range of the
engine.
24. The method of claim 23 including the steps of monitoring
pressure in the combustion chamber and controlling the outlet and
inlet valves to maintain a desired level of pressure in the
combustion chamber.
25. The method of claim 23 wherein the power produced by the engine
is increased by opening the intake valve for a longer period of
time to allow more air to be taken into the compression chamber,
and injecting more fuel into the combustion chamber to maintain the
temperature of the burning gas at the substantially constant level
even though more air is taken into the compression chamber and
delivered to the combustion chamber.
26. The method of claim 23 including the step of boosting the
pressure of the air to a level above atmospheric pressure before
the air is introduced into the compression chamber.
27. The method of claim 23 including the step of advancing the
opening of the outlet valve to maintain a desired compression ratio
in the compression chamber when more air is taken into the
compression chamber.
28. The method of claim 23 including the step of delaying the
closing of the inlet valve to allow additional gas to pass from the
combustion chamber to the expansion chamber.
29. The method of claim 23 including the step of delaying the
opening of the exhaust valve to allow pressure in the expansion
chamber to reach a level at or near atmospheric pressure before the
exhaust valve opens.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention pertains generally to internal combustion engines
and, more particularly, to an internal combustion engine and method
capable of operating with high efficiency over a wide range of
engine speeds and load conditions.
2. Related Art
Heretofore, engines have been designed for specific uses. Gasoline
engines may, for example, be designed to maximize power or
efficiency. Attempts to set the valving, stroke, and fuel delivery
at targets that provide both power and efficiency are, by design,
compromises of both. When different load conditions are factored
in, the compromises may become even greater.
With today's engines, there is much concern about pollution and the
high cost of fuel. To find a solution to these concerns, it is not
only necessary to develop an engine that is non-polluting, but also
one which is high in fuel efficiency. For fuel efficiency, it is
desirable to provide an engine that is not only efficient at one
particular load, but rather over a wide range of operating and load
conditions.
OBJECTS AND SUMMARY OF THE INVENTION
It is in general an object of the invention to provide a new and
improved internal combustion engine and method.
Another object of the invention is to provide an internal
combustion engine and method of the above character which operate
efficiently over a wide range of operating and load conditions.
The engine has compression and expansion chambers of variable
volume and a combustion chamber between the compression and
expansion chambers. A variable outlet valve controls communication
between the compression chamber and the combustion chamber, and a
variable inlet valve controls communication between the combustion
chamber and the expansion chamber. A fuel injector or other fuel
inlet introduces fuel into the combustion chamber to form a mixture
of fuel and air which burns and expands to drive an output member
in the expansion chamber. Intake and exhaust valves control the
intake of air to the compression chamber and the discharge of
exhaust from the expansion chamber, and in the disclosed
embodiments, those valves are also variable.
The engine also has temperature and pressure sensors for monitoring
temperature and pressure conditions in the compression, combustion
and/or expansion chambers and a computer responsive to the
temperature and pressure conditions for controlling the opening and
closing of the valves and the introduction of fuel into to the
combustion chamber to optimize engine efficiency over a wide range
of engine load conditions.
In some embodiments, the temperature within the combustion chamber
is maintained at a substantially constant level throughout the
operating range of the engine, and the power produced by the engine
is determined by the amount of air passing through the engine.
In others, the relative volumes of the compression and expansion
chambers and the timing of the valves are such that the pressure in
the combustion chamber remains substantially constant throughout
the operating cycle of the engine, and the exhaust is discharged at
or very close to atmospheric pressure regardless of the load on the
engine. In those embodiments, adjustments for power level or load
are made by increasing or decreasing the temperature of the burning
gas in the combustion chamber.
In some disclosed embodiments, the compression and expansion
chambers are cylinders with reciprocating pistons in them. The
pistons are connected to a crankshaft for reciprocating movement
between top and bottom dead center positions in the cylinders. The
combustion chamber is a separate chamber in which the fuel is
burned, and there is no burning of fuel either in the compression
cylinder or in the expansion cylinder. Expansion of the hot gas
from the combustion chamber drives the piston in the expansion
cylinder and produces the reciprocating motion of the pistons.
The volumes of the compression and/or expansion cylinders with the
pistons at top dead center are very small. In one embodiment, the
valves are rotary valves that do not extend into the cylinders and
can remain open without interfering with the pistons as they travel
to their top dead center positions close to the head. In some
embodiments, the piston travels to within less than 0.150 inch from
the head of the cylinder, and in some the distance is less than
0.015 inch.
The opening of the intake valve is delayed until after the piston
in the compression cylinder has passed top dead center to prevent
compressed gas from being blown back out through the intake
manifold, which would waste the work done in compressing the air
and compromise the efficiency of the engine. The delay in opening
the valve can range from about 2 degrees to 45 degrees of
crankshaft rotation, depending upon the compression ratio of the
engine and the amount of air to be taken in.
The engine can have a compression ratio in the range of about 6:1
to 24:1, and in some embodiments, greater efficiency is provided
with a compression ratio in the range of about 10:1 to 18:1. In
some embodiments, where the maximum burn temperature is held to
less than about 1800.degree. K. to prevent NO.sub.X from forming,
greater efficiency is provided with a compression ratio in the
range of about 10:1 to 16:1.
Unlike conventional reciprocating piston engines with combustion in
the cylinders, the compression ratio is determined in part by when
the outlet valve opens to release compressed air from the
compression cylinder to the combustion chamber. That generally
happens when the compression piston has completed about 90% to 95%
of its upward travel, with the point of opening being higher at
higher compression ratios. As a result, the minimum volume of the
compression cylinder is not limited by the compression ratio, and
the piston can travel to a higher point in the cylinder than
pistons in engines where combustion occurs in the cylinders and the
compression ratio is determined by the volume above the pistons at
the top of their stroke.
The amount of air and fuel provided to the combustion chamber can
be adjusted for different load conditions. The timing for the
intake valve controls the amount of air taken into the engine, and
the timing of the outlet valve assures that the compressed air is
at the correct pressure when the air is pushed into the combustion
chamber. The timing for the inlet valve and the exhaust valve can
also be adjusted according to the load. In some embodiments, the
same amount of air is pumped into the compression chamber at
different loads, but the amount of fuel injected and the amount of
gas admitted to the expansion chamber are reduced at lower loads.
The inlet valve to the expansion chamber is allowed to remain open
for a shorter period of time at lower loads, with the pressure in
the expansion chamber reaching atmospheric pressure before the
piston reaches bottom dead center. This results in below
atmospheric pressure as the piston continues its downward cycle,
but the opening of the exhaust valve is delayed past bottom dead
center to allow this negative work to be recovered during the
upward cycle of the piston. In this way, efficiency is maintained
across a wide range of load conditions.
In some embodiments, compression release braking is provided using
either or both the compression cylinder and expansion cylinder. In
one embodiment, compressed air is allowed to escape from the
compression cylinder into the intake manifold to provide
compression release braking without requiring an external muffler.
In another embodiment, compression release braking is provided
using both the compression cylinder and expansion cylinder in a
manner that allows air to be compressed in at least one cylinder on
every revolution of the crankshaft.
In some embodiments, the combustion chamber allows fuel to be
ignited and then diluted with additional air to produce a leaner
fuel mixture and reduce the production of CO. The combustion
chamber also provides a relatively long burn time to reduce the
production of CO. In some embodiments, the temperature of the
combustion chamber is between about 1400 and 1800.degree. K., which
is hot enough to ensure that all of the burn products are oxidized
and cool enough to prevent the formation of NO.sub.X. Consequently,
the exhaust from the engine is essentially free of CO and NO.sub.X.
The long burn time is beneficial in preventing unburned
hydrocarbons and soot from being discharged in the exhaust.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic diagram of one embodiment of an
internal combustion engine incorporating the invention.
FIGS. 2A-2E are diagrammatic views illustrating the operation of
the embodiment of FIG. 1.
FIG. 3 is a cross-sectional view, somewhat schematic, of an
embodiment of a four cylinder, constant pressure, reciprocating
piston internal combustion engine incorporating the invention.
FIGS. 4-7 are flow charts for different phases in the operation of
one embodiment of an engine incorporating the invention.
FIG. 8 is a graphical representation of the relative torque,
horsepower and fuel consumption for one example of an engine
incorporating the invention and representative engines of the prior
art operating under comparable conditions.
FIG. 9 is a fragmentary cross-sectional view of one embodiment of a
cylinder with a piston having a configuration for maximizing the
compression ratio in an engine with rotary valves in accordance
with the invention.
FIG. 10 is a fragmentary cross-sectional view of another embodiment
of a cylinder with a piston having a configuration for maximizing
the compression ratio in an engine with rotary valves in accordance
with the invention.
FIG. 11 is a side elevational view of another embodiment of a
piston for use in the embodiment of FIG. 10.
FIG. 12 is a simplified schematic diagram of embodiment of an
internal combustion engine incorporating the invention which
operates in a constant temperature mode.
FIG. 13 is a simplified schematic diagram of one embodiment of an
internal combustion engine according to the invention with turbo
charging.
FIG. 14 is a graphical representation of the relative pollution
products produced by an engine incorporating the invention and by
other engines.
DETAILED DESCRIPTION
In the embodiment illustrated in FIG. 1, the engine has a
compression cylinder 11 and an expansion cylinder 12 which
communicate with opposite ends of a combustion chamber 13, with
reciprocating pistons 14, 16 in the two cylinders forming chambers
of variable volume. The pistons are connected to a crankshaft 17 by
connecting rods 18, 19 for movement in concert between top dead
center (TDC) and bottom dead center (BDC) positions in the
cylinders, with each of the pistons making one upstroke and one
downstroke during each revolution of the crankshaft. The terms
upstroke and downstroke, as used herein, refer to the direction of
piston movement toward the positions of minimum and maximum
cylinder volume, not the physical directions in which the pistons
travel.
Compression cylinder 11 receives fresh air through an intake valve
21 and communicates with the inlet end of combustion chamber 13
through an outlet valve 22. Fuel is injected into the combustion
chamber through a fuel injector 23 or other suitable fuel inlet,
where it is mixed with the air from the compression cylinder. The
mixture burns and expands in the combustion chamber, and the
expanding gas flows into the expansion cylinder from the outlet end
of the combustion chamber through an inlet valve 24. Exhaust gas is
discharged from the expansion cylinder through an exhaust valve
26.
A combustion chamber which is particularly suitable for use in this
embodiment and others is described in detail in Ser. No.
11/372,737, filed Mar. 9, 2006, the disclosure of which is
incorporated herein by reference. That chamber is elongated and, in
some embodiments, folded back upon itself, with a rough, twisting
interior side wall. The chamber is a double wall structure which,
in one embodiment, has an outer wall of structurally strong
material such as steel and/or a composite material and a liner of
thermally insulative ceramic material, with long, sharp protrusions
that extend inwardly from the side wall and form hot spots which
help to provide complete combustion of the fuel mixture throughout
the chamber.
The valves are rotary valves, electronic valves, or other suitable
valves which permit a wide range of adjustment in the timing of the
valves. A rotary valve system which is particularly suitable for
use in this embodiment and others is disclosed in Ser. No.
11/372,978, filed Mar. 9, 2006, the disclosure of which is
incorporated herein by reference. The opening or closing positions
of the valves can be varied independently of each other, i.e., the
opening positions can be adjusted without affecting the closing
positions, or the closing positions can be adjusted without
affecting the opening positions. In addition, the intake, outlet,
inlet, and exhaust valves can all be adjusted independently of each
other and while the engine is running. This full adjustability of
the valve system permits continuous matching of engine performance
with every combination of load and speed.
Unlike the poppet valves traditionally used in conventional Otto
and Diesel engines, the valves employed in the invention do not
protrude into the cylinders when they are open. Consequently, the
engine can have nearly perfect volumetric efficiency, with the
volume above the pistons being very close to zero both at the end
of the compression stroke and at the beginning of the expansion
stroke. Having the minimum volumes of the cylinders near zero
allows for significant improvement in the efficiency of the
engine.
With valves that do not protrude into the cylinders, the only
limitation to full piston travel is the need for a small tolerance
or clearance to prevent the pistons from striking the head due to
thermal expansion or extension at higher engine speeds. This
clearance can, for example, be on the order of about 0.010 inch to
0.200 inch, and typically does not need to be more than about 0.015
inch. Hence, the minimum volumes of the cylinders can be much
closer to zero than they are in other engines.
Moreover, unlike conventional reciprocating piston engines where
combustion takes place in the same cylinders as compression and
expansion, the travel of the piston toward the top of the cylinder
is not limited by the compression ratio. In a conventional engine,
that ratio is determined by the ratio of the cylinder volume at
bottom dead center (BDC) to the volume at top dead center (TDC),
the need to keep the ratio below a certain level to avoid
predetonation limits how close the pistons can come to the cylinder
heads. In the engine of the invention, where the compression ratio
is determined primarily by the timing of the valves and combustion
occurs outside the compression cylinder, the compression ratio does
not limit the travel of the pistons, and the compression piston can
travel almost completely to the head because the outlet valve is
opened to discharge the compressed air to the combustion chamber
once the correct pressure has been achieved.
Although a rotary valve has the ability to open when the piston is
at top dead center (TDC), that is generally not the most desirable
way to operate the valves since it can result in compressed gases
being blown out through the intake manifold. Opening the intake
valve at top dead center would allow compressed air to escape,
thereby wasting the work done in compressing it and compromising
the efficiency of the engine.
Instead, it is preferable to retard the opening of the intake valve
until the air in the cylinder has expanded enough to be at or near
atmospheric pressure. In this way, the work done to compress the
gas is recovered as the gas pushes against the piston during the
initial portion of its downstroke.
For example, an engine with a 12.5:1 compression ratio and a 3.76
inch stroke may have a 0.015 inch clearance between the crown of
the piston and the cylinder head. If the intake valve were opened
at TDC, gas at a pressure of 504 PSI would escape and be wasted.
If, however, the opening of the intake valve is delayed until the
piston has moved down to the point where the gas has expanded to
12.5 times the volume at TDC, then the pressure of the gas above
the piston would be at or near atmospheric, no gas would be lost
out the intake valve, and the engine would still have the same
amount of air in the cylinder at BDC even with the delayed opening
of the intake valve.
In the foregoing example, the volume of the gas has expanded to
12.5 times the TDC volume when the piston has traveled
11.5.times.0.015 inch, or 0.173 inch, which is 4.6 percent of the
3.76 inch stroke and corresponds to 21.5 degrees of crankshaft
rotation. With this delayed opening, the slotted openings in the
intake valves can be substantially narrower, with the leading edges
of the openings being moved back. In other embodiments, the intake
valve may open when the compression piston has traveled past top
dead center by a distance on the order of about 2 degrees to 45
degrees of crankshaft rotation.
The engine runs because the product of the volume and the pressure
of the gas sent to the expansion cylinder is greater than the
product of the pressure and the volume of the air delivered to the
combustion chamber from the compression cylinder. Ignoring losses,
the gas entering the expansion cylinder is at the same pressure as
the air leaving the compression cylinder, but at a greater volume
by an amount proportional to the rise in temperature in the
combustion chamber. That rise is proportional to the amount of fuel
injected into the combustion chamber.
The burning of fuel in the engine can easily result in a volumetric
expansion of 2:1, which suggests that the expansion cylinders
should have twice the volume of the compression cylinders. This can
be accomplished by using a greater bore and/or stroke in the
expansions cylinders, by using a greater number of expansion
cylinders or by a combination thereof. While that would work well
at full load, it would not be as efficient when the engine is
operating at less than full load. Efficiency would be compromised
most of the time since engines are rarely operated at 100% of their
maximum load capability. In the invention, the sizes of the two
pistons can be made equal, as can their strokes, which maintains
good mechanical balance, and the amount of air intake can be varied
to match the specific needs of the engine under different operating
conditions. Thus, for example, with the conditions stated above
(equal numbers of compression and expansion cylinders, pistons of
equal size and stroke, and a maximum expansion ratio of 2:1 at full
load), the air intake to the compressor is limited to about 50%. If
the expansion ratio at full load is other than 2:1, then the amount
of air intake can be adjusted accordingly, e.g. 40% for a ratio of
2.5:1. With lesser loads and lower power output, less air can be
compressed, and less air requires less fuel to produce the same
percent of expansion. Less air and less fuel produce less net power
for smaller loads. Since the engine recaptures compressed air and
work done against atmospheric pressure, there is no decrease in
efficiency at partial loads.
The engine is not, however, limited to having equal numbers of
compression and expansion cylinders and pistons of equal size and
stroke. It can have any combination of cylinders and piston sizes
and strokes desired and, by adjustment of the air intake and other
valves, still maintain optimum efficiency throughout its operating
range. The engine can also have more than one combustion chamber
between the compression and expansion cylinders, if desired.
The engine can have virtually any compression ratio because, unlike
an Otto cycle engine, there is no fuel to predetonate in the
cylinder doing the compression, which would limit the compression
ratio to about 10:1, and unlike a typical Diesel engine, the
compression ratio does not have to be higher than about 18:1 in
order to generate enough heat to ensure detonation. The engine can
operate with a compression ratio anywhere in the range of about 6:1
to 24:1, but has the greatest efficiently with a ratio of about
10:1 to 18:1, although to prevent NO.sub.X from forming, the
maximum temperature should be held to about 1700.degree.
K.-1800.degree. K. Under those conditions, the engine produces
maximum fuel efficiency with a compression ratio in the range of
about 9:1 to 14:1. The engine can also operate at other compression
ratios, but possibly not as efficiently. In areas where NO.sub.X
pollution standards are not as stringent, the efficiency of the
engine can be increased by the use of a higher compression
ratio.
The compression ratio is controlled by the timing of the intake,
outlet and inlet valves. In typical operation, the outlet valve
opens when the pressure above the piston in the compression
cylinder equals the pressure in the combustion chamber. In an
engine having a 9:1 compression ratio in which the compression
cylinder is allowed to have a full charge of air, the outlet valve
opens when the piston has completed slightly more than 90% of its
upward travel toward top dead center. For other compression ratios
on the order of 10:1 to 18:1, the outlet valve is opened when the
compression piston has completed about 90% to 95% of its upward
travel, with the point of opening being higher at higher
compression ratios. If the compression cylinder is not allowed to
have a full charge of air, then the pressure within the cylinder
will rise more slowly, and the outlet valve will open later in the
upward stroke. Regardless of when the outlet valve is opened, it
closes at or near top dead center for maximum efficiency.
The operating cycle of the engine is illustrated in FIGS. 2A-2E. In
this particular embodiment, expansion piston 16 leads compression
piston 14 by a few degrees, and the opening of inlet valve 24 is
timed to coordinate with the opening of outlet valve 22, which
maintains a substantially constant pressure in combustion chamber
13. That pressure is typically on the order of 200 to 1000 PSI and
is dependent upon the compression ratio. Thus, it might, for
example, be on the order of 270, 370 and 840 PSI for compression
ratios of 8:1, 10:1 and 18:1, respectively.
If desired, for maximum engine balance, the two pistons can be
timed to be precisely in phase and to reach top dead center at the
same time. That will require the inlet and outlet valves to open at
slightly different times, which will cause some pressure pulsing.
However, the pressure pulses are relatively small due to the
relatively large volume of the combustion chamber compared to the
volume of air being provided by the compression chamber. Hence, the
pulsing will not appreciably affect the efficiency of the
engine.
The amount of lead between the expansion and compression pistons
depends upon the compression ratio of the engine. With a
compression ratio of 12.5:1, for example, the expansion piston
leads by approximately 15 degrees of crankshaft rotation. With
lower compression ratios, the lead time is greater, and for higher
compression ratios, it is less.
As illustrated in FIG. 2A, at the start of the operating cycle,
compression piston 14 is at top dead center, expansion piston 16 is
15 degrees past top dead center, and the compression cylinder
valves are closed. As the compression piston begins its downward
stroke, intake valve 21 opens as shown in FIG. 2B, and air is drawn
into the compression cylinder. Under normal operating conditions,
the engine operates most efficiently when the intake valve is open
for an amount of time such that after the volumetric expansion
produced by the burning of the fuel in the combustion chamber and
the decrease in pressure due to expansion of the gas in the
expansion cylinder, the final pressure at the end of expansion will
be close to atmospheric pressure. Keeping the exhaust pressure
close to atmospheric pressure reduces the amount of energy wasted
and provides for maximum efficiency. The exhaust valve is typically
opened when the pressure is between atmospheric pressure and about
20% above atmospheric pressure, and in one presently preferred
embodiment, it is opened when the pressure is about 2 PSI above
atmospheric pressure, although that can vary somewhat with RPM as
shorter stroke times require more force to get the exhaust out. The
exhaust pressure is usually not allowed to go below atmospheric
pressure since that would waste work.
While under most conditions, it is desirable to vary the timing of
the valves for different loads so that the exhaust pressure remains
close to atmospheric pressure, that is not the case when it is
desired to maximize power output and sacrifice efficiency for a
brief period of time, such as when accelerating a vehicle on the
entrance ramp to a freeway. In an engine having an expansion ratio
of 2:1, for example, the exhaust pressure at BDC might rise to
about 15 PSI over atmospheric pressure at maximum power output, and
in a lower compression engine having an expansion ratio of 3:1, it
might rise to about 30 PSI above atmospheric pressure. The ability
to increase power in this manner is useful, and the sacrifice in
overall fuel economy is relatively insignificant since it lasts for
only a few seconds. It also permits the use of a smaller, lighter,
less expensive engine with the same peak power rating as a much
larger engine.
The amount of time the intake valve should remain open depends upon
the configuration of the engine. In a four cylinder engine with two
expansion cylinders and two compression cylinders of equal bore and
stroke, for example, the engine operates most efficiently under
normal conditions when the intake valve is open for about 40% of
the downward stroke of the compression piston. In this example, an
expansion ratio of 2.5:1 would allow the exhaust pressure in the
expander to be about equal to atmospheric pressure at when the
expansion piston is at BDC and the engine is operating at full
load.
With an engine having two compression cylinders and four expansion
cylinders where all six cylinders are of equal bore and stroke, the
basic operation of the engine is the same, but the timing of the
valves is different to allow the compression cylinders to take in
more air. Thus, the six cylinder engine operates most efficiently
when the intake valve is open for about 80% of the downward stroke
so that with an expansion of 2.5 in the combustion chamber the
pressure in the expander will go to atmospheric pressure at BDC
when the engine is operating at full load. In the paragraphs which
follow, it is assumed that the engine is a four cylinder engine,
with cylinders of equal size, and that the intake valve is open for
40% of the downward stroke. When the intake valve closes, the
piston continues its downward travel, as illustrated in FIG.
2C.
During the remaining 60% of the downward travel of the compression
piston, a subatmospheric or negative pressure is developed in the
cylinder above the piston, and that requires work. However, the
pressure in the crankcase below the piston typically remains at or
above atmospheric pressure, and the work is recovered during the
first 60% of the upward stroke when the piston is pushed in the
upward direction by the higher pressure below it.
As the compression piston continues its upward travel, the air in
the cylinder above it is compressed, and when the pressure in the
cylinder reaches the pressure in combustion chamber 13, outlet
valve 22 opens as illustrated in FIG. 2D, and the piston pushes the
compressed air into the combustion chamber. The outlet valve closes
when the compression piston is at or near top dead center, as seen
in FIG. 2A.
Inlet valve 24 opens at approximately the same time as outlet valve
22, and the expanding gas is transferred from combustion chamber 13
to expansion cylinder 12, driving expansion piston 16 in a downward
direction. The inlet valve remains open until the volume of gas
entering expansion cylinder 12 substantially equals the amount of
air compressed in compression cylinder 11 times the expansion ratio
in the combustion chamber. The amount of expansion is dependent
upon the amount of fuel burned per unit of air, and that is
determined by the load encountered by the engine.
At full load, for example, with a compression ratio of 9:1, an
expansion ratio of 2.5:1 can occur in the combustion chamber with a
maximum burn temperature of approximately 1700.degree. K. In this
example, the outlet valve will be open for approximately the last
10%-12% of the compression stroke, and the inlet valve will be open
for approximately the first 25%-30% of the expansion stroke.
At higher compression ratios, the temperature of the compressed gas
is higher, and the pressure in the combustion chamber is higher. To
get to the higher compression pressure the outlet valve opens
later. With the higher pressure, the inlet vale closes sooner so
that when the gas is fully expanded at BDC, it will be at or close
to atmospheric pressure.
The expansion ratio which can be used with a given compression
ratio is limited by the maximum combustion temperature that can be
used without creating pollution. With a compression ratio of
13.5:1, for example, a compression temperature of 850.degree. K.
will rise to 1700.degree. K. with an expansion ratio of 2:1,
whereas with a compression ratio of 10:1 and a maximum burn
temperature of 1700.degree. K., an expansion ratio of 2.25 can be
used.
The compression piston does work during the compression of the air
and when it is pushing the compressed air into the combustion
chamber. The expansion piston provides full pressure work output
for approximately the first 25%-30% of its downward stroke and then
continues providing work output as the pressure in the cylinder
drops to approximately atmospheric pressure as the piston completes
its travel to bottom dead center.
When the expansion piston is at or near bottom dead center, exhaust
valve 26 opens, as shown in FIG. 2E, and thereafter the rising
expansion piston pushes the exhaust gases out into the atmosphere.
Since the exhaust valve opens when the gas in the cylinder is
essentially at atmospheric pressure, substantially no energy or
work is left in the pressure of the gas, and efficiency is
maximized. The exhaust valve closes as the expansion piston
approaches top dead center, and the cycle repeats.
A distinctive feature of the invention is the ability to adjust the
valves to make the pressure in the expansion cylinder close to
atmospheric pressure when the exhaust valve is opened with
different loads, thereby maximizing efficiency over a wide range of
operating conditions.
As discussed above, some pressure is required to push the gas out
of the expansion cylinder, and the target pressure at bottom dead
center is therefore typically a couple of PSI above atmospheric
pressure. This allows for a shorter expansion stroke than otherwise
would be necessary, and engine size can thus be reduced without
loss of efficiency.
At lower load conditions, the combustion chamber temperature (burn
temperature) is reduced, the expansion of the gas is reduced, and
the inlet valve is open for a proportionately shorter period of
time. Thus, the total work output is reduced with a smaller amount
of gas going to the expansion cylinder. For example, at half load,
the fuel injected into the combustion chamber is one-half of the
amount injected at full load, and consequently the expansion is
only half of what it is with a full load. With the reduced
expansion, the inlet valve is open for a smaller portion of the
stroke, and in this example, it still opens at or near top dead
center, but it stays open for only about 17.5% of the expansion
stroke, rather than about 25%-30%. The expansion piston does useful
work until the gas in the cylinder is expanded and the pressure
drops approximately to atmospheric pressure, which in this example
occurs when the piston has traveled about 70% of its downward
stroke.
During the last part of the stroke, the expansion piston is working
against a partial vacuum and provides negative net work for that
part of the stroke. To compensate for the negative work, the
exhaust valve is kept closed during the first part of the upward
stroke, and the lost work is recovered when the higher pressure
below the piston pushes it back up. When the pressure above the
expansion piston approaches atmospheric pressure, the exhaust valve
is opened, and the exhaust gases are pushed out of the cylinder by
the piston as it completes its upward stroke. In the example given,
the exhaust valve opens when the piston has moved 30% of its upward
travel. With the exhaust valve being opened at atmospheric
pressure, no work is lost, and efficiency is maintained. Opening
the exhaust valve near atmospheric pressure also avoids loud
exhaust noises and can allow the engine to operate without a
muffler. Moreover, with factors such as a longer burn time, no
cooling of the combustion chamber walls, and good temperature
control, the exhaust is much cleaner than in typical Otto and
Diesel engines, and consequently the engine may not need a costly
catalytic converter either.
The engine is started by introducing air into the compression
cylinder, compressing it, pumping the compressed air into the
combustion chamber, heating it, and allowing the expanded gas to
flow through the inlet valve into the expansion cylinder. This is
similar to the normal operation of the engine except that it can be
done at very low pressures, e.g. 2-4 atmospheres. The lower
pressure can be provided by opening the outlet valve sooner than
usual and/or by closing the intake valve sooner, although this may
not be as efficient. As air is passed into the combustion chamber
and heated, then expanded in the expansion cylinder, the engine
will start to develop a work output which is used to keep the
engine running. As the engine starts to run, the inlet valve will
allow less than the normal amount of gas to enter the expansion
cylinder, and that causes the pressure in the combustion chamber to
increase until normal operating pressures are obtained. This
provides easier starting and the use of a smaller starting
motor.
Since the outlet valve of the compression cylinder opens when the
pressure in that cylinder reaches the pressure of the gas in the
combustion chamber, by varying the timing of the inlet valve, the
outlet valve, the intake valve, or a combination thereof, the
pressure in the combustion chamber can be built up to the normal
level necessary for the running of the engine.
When the combustion chamber pressure increases to its normal level,
the engine begins normal operation, with the timing of the valves
returning to normal running conditions.
Since the engine can maintain the correct or optimum combustion
chamber pressure by varying valve timing, the engine can compensate
for situations where normal engine breathing is limited with no
loss in performance. Such conditions exist, for example at high
altitude, high ambient temperature, and low atmospheric pressure as
well as at higher engine RPM. At high altitude, the air is less
dense, the barometric pressure is lower, and the reduction in air
pressure would normally cause less air mass to be drawn into the
compression cylinder. At high ambient temperatures, the density of
the air is lower than it would be at normal temperatures, and less
air mass would likewise be drawn into the compression cylinder.
However, since only a portion of the capacity of the compression
cylinder is utilized under normal operating conditions, it is
possible to allow the intake valve to be open for a longer period
of time when a high ambient temperature or a decrease in barometric
pressure is detected. Thus, for example, instead of opening the
intake valve for 40% of the intake stroke, it can be opened for 50%
or 60% of the stroke as needed, and this extra capacity will allow
a greater volume of air to be drawn into the cylinder and
compressed to compensate for the air being less dense. The ability
to draw in additional air can also be used to compensate for
breathing losses that occur at high RPM. The net result in each of
these cases is that the same mass of air will be drawn into the
engine for any specific load, the same amount of work will be
required to compress it, and the same work output will be
maintained even though the density of the air is less at high
altitude or high temperatures and also when breathing is more
difficult at high RPM. In this way, the performance of the engine
is maintained over a wide range of ambient conditions without any
decrease in efficiency or performance.
Under lower load conditions, the same amount of air is still pumped
into the compression cylinder, but less fuel is burned in the
combustion chamber. Gas expansion is thus reduced, the inlet valve
is allowed to remain open for a shorter period of time, and the
work output of the expansion piston is reduced. Under these
conditions, the pressure in the expansion cylinder will reach
atmospheric pressure before the expansion piston reaches bottom
dead center, and negative work is once again done. However, as
discussed above, that work is recovered by delaying the opening of
the exhaust valve and allowing the higher pressure below the piston
to push it up. Once the gas has been compressed back to atmospheric
pressure, the exhaust valve is opened to let the gas out.
Thus, the difference in running at partial load is that less fuel
is used to heat the mixture in the combustion chamber. With the
same amount of air, less fuel produces less heating, and less
heating produces less expansion. The reductions in heating and
expansion are compensated for by opening the inlet valve for a
shorter period of time and by delaying the opening of the exhaust
valve. In this way, the efficiency of the engine is maintained
throughout the load ranges of the engine.
The engine can be turned off or shut down by turning off the fuel
supply or by closing the valves. No work output can occur under
those conditions, and the pressure in the combustion chamber will
be maintained for some period of time. The pressure stored in the
combustion chamber provides quick and easy restarting of the
engine, and it also allows the engine to idle at zero RPM, e.g.
when the vehicle in which it is installed is stopped at a stoplight
and valves which can be closed independently of crankshaft rotation
are used.
If all of the valves are closed when the expansion piston is at top
dead center, the pistons will not be under pressure to move, and
the pressure and temperature will be maintained in the combustion
chamber. Since that chamber is well insulated, it will not lose
significant temperature or pressure for several minutes. During
that time, the engine is not turning, and it is effectively idling
at zero RPM.
When valves which cannot seal independently of crankshaft rotation
are used, zero RPM idling is not possible. However, with rotary
valves such as those disclosed in Ser. No. 11/372,978, the engine
can idle at speeds on the order of 50-300 RPM, which is beneficial
in saving fuel, even when the valves are driven from the
crankshaft.
When power is once again desired from the engine, the valve
sequence can pick up where it left off, and hot pressurized gas
from the combustion chamber can once again enter the expansion
cylinder and do work. If the zero RPM condition is maintained for
an extended period of time, the resulting decreases in temperature
and pressure are detected by sensors in the combustion chamber, and
the engine is allowed to run for a few revolutions in order to
maintain a minimum temperature and pressure relationship in the
combustion chamber.
When used in vehicles such as automobiles, the engine will provide
some degree of braking when it is running and the vehicle is
coasting. In this situation, the amount of fuel going to the
combustion chamber is greatly reduced, and the work output
decreases to the point that the moving vehicle is turning the
engine. The frictional and breathing losses associated with turning
the engine when there is substantially no energy input from the
limited amount of fuel being burned produce mild engine braking and
a gradual slowing down of the vehicle. The amount of braking can be
increased by opening the exhaust valve when the expansion piston is
at bottom dead center so that the work input during the last
portion of the expansion stroke will not be recovered during the
exhaust stroke. Thus, the braking provided by the engine is
variable and is controlled by the timing of the valves.
The engine can also provide very effective braking in
tractor-trailer rigs and other large trucks, where valve operation
is modified to provide compression release engine braking, one well
known form of which is commonly known as "Jake braking".
Compression relief braking is much more effective than normal
engine braking and can save brake wear and reduce overheating of
the brakes, particularly on long downhill grades and steep
declines. With the invention, compression release engine braking
can be done in several ways which make it highly flexible and
adjustable.
One way to provide compression release engine braking is to close
the outlet and inlet valves and allow air to enter the expansion
cylinder though the exhaust valve during the downward stroke of the
expansion piston. The exhaust valve is closed at or near bottom
dead center, and the expansion piston then does work while
compressing the air in the expansion cylinder during the upstroke.
That work slows down the engine and the vehicle. The point at which
the exhaust valve opens can be adjusted to provide the amount of
braking desired. The opening of the exhaust valve releases the
pressure and thereby wastes the work which has been done. The
sudden release of the compressed air may produce a considerable
amount of noise that comes out the exhaust system, which may
require the use of a muffler that otherwise might not be required
in normal operation of the engine.
Compression release engine braking can also be provided with the
compression cylinder by keeping the outlet valve closed, drawing
air into the compression cylinder through the intake valve for all
or part of the downstroke of the compression piston, compressing
the air during the upstroke, and then opening the intake valve to
release the pressure toward the end of the upstroke. The work done
in compressing the air slows down the engine and the vehicle, and
the amount of braking is controlled by selection of the point at
which the valve opens.
The high pressure air is discharged back into the intake manifold
which can be closed off from the atmosphere by a one-way flapper
valve at the air inlet. Since the manifold is larger than the
compression cylinder, the pressure of the air is reduced, and the
manifold is filled with air at a relatively low pressure. During
this method of compression release engine braking, this same air is
moved back and forth between the manifold and the compression
cylinder, and no dirt can be sucked back into the cylinder from the
manifold because the intake manifold is very clean. Also, since
virtually no air can leak out through the flapper valve to the
outside atmosphere, the sound of the sudden pressure release is
greatly muffled, and an external muffler may not be required.
For maximum compression release engine braking, both the
compression and expansion cylinders can be used. This can
potentially provide twice the braking force of conventional
compression release engine braking systems because conventional
engines typically compress air only once every two revolutions
whereas the invention can compress it on every revolution.
A one-way flapper valve or other suitable valve can be used to shut
off air flow in the exhaust system as well as in the intake
manifold. If that is done, the external noise produced by the
sudden release of pressure in the expansion cylinder will be
greatly reduced because the valve will dampen the sound escaping
from the engine.
During compression release engine braking, it is possible to allow
small amounts of air and fuel to move through the combustion
chamber to allow just enough burning to take place to maintain the
desired temperature and pressure so that immediate power will be
available when it is desired or needed.
In some embodiments which use rotary valves or other valve systems,
it may not always be possible to move the valves far enough and
quickly enough to fully utilize the compression release braking
capability of the engine. In this case, a small closed chamber and
valve can be added to the compression cylinder. The extra chamber
can have approximately 1/12 to 1/6 of the volume of the compression
cylinder, and when the extra valve is open, the compressed air can
enter and be stored in the extra chamber during the compression
stroke without being over pressurized and damaging the engine. The
valve remains open for as long as compression release engine
braking is being used.
When the intake valve is opened at top dead center, the compressed
air will escape to the intake manifold, and the engine will be
ready for the next cycle. When compression release engine braking
is no longer needed, the extra valve is closed, and the other
valves resume normal operation.
FIG. 3 illustrates a four cylinder engine incorporating the
invention. This engine has two compression cylinders 31, 32, two
expansion cylinders 33, 34 and a combustion chamber 35, with
pistons 36, 37 in the compression cylinders and pistons 38, 39 in
the expansion cylinders. The pistons are connected to a crankshaft
40 by connecting rods 41-44. The cylinders are formed in an engine
block 47, and the crankshaft is located in a crankcase 48 in the
lower portion of the block. The two compression pistons are 180
degrees out of phase with each other, as are the two expansion
pistons, so that one piston in each pair is on the upstroke while
the other is on the downstroke. For good mechanical balance in this
particular embodiment, the two outer pistons (compression piston 31
and expansion piston 34) are in phase with each other, as are the
two inner pistons (compression piston 32 and expansion piston
33).
Air is supplied to the compression cylinders through an intake
manifold 49 and intake valves 51, 52 in cylinder head 53. Those
cylinders also communicate with the inlet end of combustion chamber
35 via an outlet manifold 54, with communication between the
cylinders and that manifold being controlled by outlet valves 56,
57. The outlet end of combustion chamber 35 communicates with
expansion cylinders 33, 34 via an inlet manifold 59, with inlet
valves 61, 62 controlling communication between the chamber and
those cylinders. Exhaust gases are expelled from the expansion
cylinders through an exhaust manifold 63, with communication
between the cylinders and the manifold being controlled by exhaust
valves 66, 67.
As in the embodiment of FIG. 1, combustion chamber 35 can, for
example, be of the type disclosed in Ser. No. 11/372,737, and
valves 51, 52, 56, 57, 61, 62, 66 and 67 can be rotary valves of
the type disclosed in Ser. No. 11/372,978. Here again, other
suitable types of valves can be used, if desired.
Fuel injectors 68 supply fuel to the combustion chamber, with flow
separators or baffles dividing the region near the fuel inlet into
smaller volumes 69 where the fuel can mix and burn with only a
portion of the air introduced into the chamber. A safety relief
valve 71 provides protection for the combustion chamber in the
event that the pressure in the chamber should ever rise above a
safe level.
In this embodiment, air is drawn into compression cylinders 31, 32
during the intake strokes (down) of the pistons in them and is
compressed during the compression strokes (up) of the pistons.
Since those pistons are 180 degrees out of phase with each other,
there are two intake strokes and two compression strokes for each
revolution of the crankshaft.
The compressed air from cylinders 31, 32 is delivered to combustion
chamber 35 during alternate halves of the operating cycle where it
is mixed and burned with the fuel from the injectors. The expanding
gas is delivered to expansion cylinders 33, 34 during alternate
half cycles where it drives the pistons down and produces work
output.
The timing of the valves relative to the pistons in the embodiment
of FIG. 3 is the same as it is in the embodiment of FIG. 1, the
only difference being that with two compression cylinders and two
expansion cylinders, there are two intake strokes, two compression
strokes, two expansion strokes, and two exhaust strokes for each
operating cycle or revolution of the crankshaft.
In this particular embodiment, a radiator 73 is shown as being
connected to exhaust manifold 63 for cooling exhaust gases that are
low in oxygen and mixing them with fresh air from the intake if the
presence of small amounts of NO.sub.X is detected in the exhaust.
The exhaust system is also illustrated as including a muffler 74 in
this embodiment. In other embodiments, the radiator and/or the
muffler may not be required.
Temperature and pressure sensors monitor conditions throughout the
engine and provide that information to a computer 76 which controls
the delivery of fuel to the combustion chamber and the timing of
the valves in accordance with the environmental and load
conditions. Thus, temperature sensors T1-T4 and pressure sensors
P1-P4 monitor temperature and pressure in the compression and
expansion cylinders, and temperature sensors T5-T10 and pressure
sensor P5 monitor temperature and pressure in the combustion
chamber. Temperature sensors T11 and T12 monitor temperature in the
engine head and crankcase, temperature sensor T13 monitors
temperature in inlet manifold 59, temperature sensor T15 monitors
temperature in the intake manifold, and temperature sensor T14 and
pressure sensor P6 monitor temperature in the exhaust manifold. An
oxygen sensor O1 monitors the level of oxygen in the exhaust
manifold, and temperature sensors T16, T17 monitor temperature in
the cooling system for the engine.
Small chambers A1, A2 provide increased volume above compression
pistons 37, 37 to prevent over pressure in the cylinders when using
compression release engine braking. Communication between those
chambers and the cylinders is controlled by valves V1, V2.
An additional chamber A3 is also included in the intake manifold to
provide increased volume for receiving the air which is discharged
into that manifold during compression release engine braking. A
one-way flapper valve V3, or other suitable valve, controls
communication between that chamber and the air inlet, allowing
outside air to be drawn into the manifold, but preventing the
pressurized air from the compression cylinders from being
discharged to the atmosphere.
The starting routine for an engine incorporating the invention with
a compression ratio of 13:1 is illustrated in the flow chart of
FIG. 4. If the pressure in the combustion chamber is not more than
450 PSI and the engine sensor is on, the engine is in the startup
mode. As long as the pressure remains below approximately 476 PSI,
the intake, outlet, inlet and exhaust valves are set in accordance
with the pressure as fuel is injected into the combustion chamber.
When the pressure exceeds approximately 476 PSI, the engine
switches to the run mode. If the engine sensor is not on or if a
timeout occurs before the pressure exceeds approximately 476 PSI,
the engine is shut down.
The run mode is illustrated in the flow chart of FIG. 5. A table
for different engine loads is stored in memory, and if the engine
is running, the air intake and fuel delivery are set to be
proportional to the load reading as determined by the throttle
position. Air intake is set from look up tables for each load
requirement, combustion chamber pressure is monitored, and valve
timing is adjusted accordingly to maintain a virtually constant
pressure. Temperature is monitored in the combustion chamber, and
the fuel delivery is adjusted accordingly. The intake, outlet and
inlet valves are set for the load conditions, as is the exhaust
valve. This process repeats as long as the engine is running.
The routine for adjusting the intake and inlet valves is
illustrated in FIG. 6. The pressure in the combustion chamber is
monitored to see if it is within tolerances above and below 500
PSI. If the pressure is within tolerances, it is checked again
after a short time. If it is higher than tolerance, the inlet
valve(s) is (are) opened slightly, and the pressure is checked
again. If the pressure is below tolerance, the valve(s) is (are)
closed slightly, and the pressure is checked again after a short
time delay.
As illustrated in FIG. 7, the shutdown routine consists of shutting
off the fuel delivery and setting the valves to their default
angles.
With the operation of the valves and the delivery of fuel all under
computer control, the engine can be programmed or targeted for a
wide variety of different applications simply by changing the
software. The exhaust valve can, for example, be programmed to open
when the pressure in the expansion cylinder is at or near
atmospheric pressure for maximum efficiency. The temperature and
pressure in the combustion chamber are software controlled, as are
the amount of air taken into the compression chamber and the amount
of braking provided by the engine. By simple changes in software,
it is possible to trade off efficiency, power, and engine braking.
With such a wide range of control, the engine has a flexibility
that other engines do not have.
Torque, horsepower, and fuel efficiency curves for exemplary
embodiments of the engine of the invention and conventional Otto,
Diesel, and Turbo Diesel engines are shown in FIG. 8. These curves
are based upon calculations made for engines of equal air intake
(0.95 liter per revolution), with the engine of the invention
having a compression ratio of 13:1, an Otto engine having a
compression ratio of 9:1, and Diesel and Turbo Diesel engines
having a compression ratio of 19.5:1. As these curves show, the
engine of the invention produces greater torque and has a much
broader and flatter torque range than the Otto, Diesel and Turbo
Diesel engines having the same air intake per engine
revolution.
Curve 77a represents the calculated torque produced by the engine
of the invention, curve 78a represents the calculated torque
produced by an Otto engine, and curves 79a and 80a represent the
calculated torque produced by Diesel and Turbo Diesel engines. As
these curves show, the invention produces a steady torque output of
approximately 125 ft-lbs from 1600 RPM to more than 4000 RPM,
whereas the torque curves for the other engines drop off
significantly below about 1800 RPM and above about 3000 RPM, never
reaching the level of the invention. Below 1800 RPM, the Diesel
engine produces less than about 95 ft-lbs, and the Otto and Turbo
Diesel engines produce less than about 115 ft-lbs. Between 3000 and
4000 RPM, the outputs of the Otto and Turbo Diesel engines drop
below 100 ft-lbs, and the output of the Diesel engine drops to well
below 80 ft-lbs. Thus, the engine of the invention has a higher,
broader, and substantially flatter torque output than the Otto,
Diesel and Turbo Diesel engines, and may be able to use a smaller,
lighter and less expensive transmission than the other engines.
Curves 77b, 78b, 79b, and 80b represent the calculated horsepower
produced by the engine of the invention, the Otto engine, the
Diesel engine, and the Turbo Diesel engine, respectively. As these
curves show, the invention produces significantly greater
horsepower than the other engines, particularly at higher RPM.
Thus, at 1600 RPM, the invention produces about 38 HP, the Turbo
Diesel engine produces about 34 HP, the Otto engine produces about
32 HP, and the Diesel engine produces only about 25 HP. At 4000
RPM, the invention produces almost 95 HP, the Turbo Diesel engine
produces about 75 HP, the Otto engine produces about 70 HP, and the
Diesel engine produces less than 60 HP.
Curves 77c, 78c, 79c, and 80c represent the calculated fuel
efficiency of the engine of the invention, the Otto engine, the
Diesel engine, and the Turbo Diesel. This unit of measure is used
rather than the more common miles per gallon in order to provide a
more even basis for comparison since Diesel fuel is heavier and
contains more energy per gallon than gasoline. Fuel efficiency was
calculated as the product of a constant, horsepower and time
divided by the number of pounds of fuel consumed. Although the
engine of the invention can run on either gasoline or Diesel fuel,
the calculations were based upon the use of gasoline in it and in
the Otto engine and Diesel fuel in the Diesel and Turbo Diesel
engines. As these curves show, the engine of the invention produces
about 45 HP-hours per pound throughout its operating range, whereas
the other three engines produce no more than about 35 HP-hours per
pound and fall off at higher RPM. Thus, the engine of the invention
uses approximately 30 percent less fuel to do the same work as the
other engines, which means that the operating expense of the engine
will be significantly less than that of the other engines.
As illustrated in FIGS. 9-11, the pistons can be configured to
reduce the volumes of the cylinders when the pistons are at top
dead center and thereby increase the compression ratio of the
engine. This may provide a significant advantage over conventional
engines with poppet valves which open into the cylinders and limit
the upward travel of the pistons.
In the embodiment of FIG. 9, rotary valves 81 protrude into the
upper portion of cylinder 82, and semicylindrical recesses 83 are
formed in the upper portion of piston 84 to receive the protruding
portions of the valves when the piston is in the top center
position. This permits the piston to travel almost to the top of
the cylinder, reducing the volume of the cylinder almost to zero
and thereby increasing power output and improving the efficiency of
the engine.
In the embodiment of FIG. 10, the rotary valves 81 are recessed in
ports 86 in cylinder head 87, and piston 88 is formed with
projections 89 which extend into the lower portions of the ports.
The projections have concave upper surfaces 91 which mate with the
curvature of the valves to minimize the volume above the piston in
the top dead center position.
The piston 92 shown in FIG. 11 is similar to piston 88 with
protrusions 93 which extend into the lower portions of the ports.
However, piston 92 differs from piston 88 in that the upper
surfaces 94 of piston 92 are slightly rounded or convex in order to
avoid any possibility of a gas lock occurring between the piston
and the valves. Alternatively, the upper surfaces of the
projections can be made flat or even concave as long as the
curvatures of the protrusions and the valves do not match so
closely that gases can become trapped between the piston and the
valves.
The engine can operate with leaner fuel mixtures than other
engines, which provides a significant increase in fuel efficiency.
It is able to do so because there is no burning of the fuel in the
compression and expansion cylinders and, therefore, no chance of
burning holes in those pistons as can happen with lean burning in
other engines. In a typical embodiment with the segmented
combustion chamber, as little as 10 percent of the air going
through the chamber needs to support combustion. After burning, the
lean mixture is mixed with the other 90 percent of the air, and the
gas leaving the combustion chamber has an average temperature that
is equivalent to having a burn that was 10 times leaner. The lean
burn works well in this engine and is useful for low load, low RPM
conditions such as idling. Running lean also generates more heat
per unit of fuel and, thus, provides higher efficiency.
In other embodiments, as much as 100% or as little as about 3% of
the air passing through the combustion chamber may be used to
support combustion. At full power, all the air is used to support
combustion, and fuel is injected into all of the segments of the
combustion chamber. That does not, however, mean that all of the
oxygen is used because the engine runs lean and the burn
temperature is held down, e.g. to about 1800.degree. K. in order to
prevent pollution. At very low idle speeds, as little as about 3%
of the air may be required to maintain the desired idle speed and
to keep the burn temperature at a high enough level, e.g. above
1400.degree. K., to prevent the production of CO.
As discussed more fully hereinafter, the engine can also maintain a
constant temperature without a segmented combustion chamber or air
bypass by using the valves to control the amount of air flowing
through the engine per revolution.
The engine can also take in large quantities of air at high RPM.
This can provide a significant advantage over engines in which the
time available to get a full charge of air decreases
proportionately at higher engine speeds. With less air in the
cylinder at bottom dead center in a standard engine, not only is
there less air available to burn fuel, but the effective
compression ratio is also reduced, and that reduces the efficiency
and the total work output of the engine. The increased air input at
higher RPM is possible because the engine normally does not use all
of the air that is available. The intake valve normally closes
before the compression piston reaches bottom dead center in order
to limit the amount of air taken in and thus provide the correct
amount of gas to the expansion cylinder after it is heated and
expanded in the combustion chamber. By keeping the intake valve
open longer, the engine can provide additional air intake at higher
RPM while keeping the compression ratio and efficiency constant.
With the efficiency remaining constant, the horsepower produced by
the engine continues to increase with increased RPM.
With all of the burning taking place away from the pistons, there
is no possibility of the pistons outrunning a flame front
regardless of the speed of the engine. Moreover, there are no slow
acting springs in the valve system, and there is no valve float to
compromise compression or cause parasitic pressure losses that
waste engine power. Full burning of the fuel supplied not only
gives the engine high efficiency at high engine speeds, but also
ensures that all of the energy of the fuel goes into supplying
additional horsepower at high RPM, which is not the case in other
engines.
Valve timing and efficiency can be changed by software, and the
engine can trade efficiency for additional horsepower when needed.
High efficiency is obtained, inter alia, by exhausting at or near
atmospheric pressure and by controlling the valves accordingly. If
additional power is desired, the intake valve can be timed to let
in more air which can burn more fuel and produce exhaust pressures
which are above atmospheric pressure. The tradeoff between
efficiency and power is especially useful for short periods of
time, such as when accelerating a vehicle onto a freeway. This
temporary loss of efficiency may actually result in an overall
improvement in efficiency if the availability of reserve power
permits a smaller, lighter and less expensive engine to be
used.
In the embodiments described thus far, the engine can be thought of
as a constant airflow engine, with the amount of gas passing though
the combustion chamber being substantially constant at any given
engine speed, or RPM, and the power output being controlled by
varying the burn temperature or heat of the gas in the combustion
chamber.
Under most operating conditions and loads, the engine can also be
operated in a constant temperature mode in which the temperature
within the combustion chamber is maintained substantially constant
throughout the operating range and the power level is controlled by
adjusting the amount of air passing through the engine. Such an
embodiment is illustrated in FIG. 12.
The embodiment of FIG. 12 is similar to the embodiment of FIG. 1 in
that it has a compression cylinder 11, an expansion cylinder 12 and
a combustion chamber 13, with reciprocating pistons 14, 16 forming
chambers of variable volume in the two cylinders. The pistons are
connected to a crankshaft 17 by connecting rods 18, 19. An intake
valve 21 controls the flow of fresh air to the compression
cylinder, and communication between the compression cylinder and
the combustion chamber is controlled by an outlet valve 22. Fuel is
injected into the combustion chamber through a fuel injector 23,
and communication between the combustion and the expansion cylinder
being controlled by an inlet valve 24. The flow of exhaust gas from
the expansion cylinder is controlled by an exhaust valve 26. As in
the other embodiments, the valves are all adjustable, with variable
opening or closing times, and can, for example, be rotary valves of
the type described in detail in Ser. No. 11/372,978. However, as in
the other embodiments, they can also be electronic valves or other
types of variable valves if desired.
Temperature sensors 96 and pressure sensors 97 monitor the
temperature of the burning mixture and the pressure in the
combustion chamber, and that information is provided to a computer
98 which controls the amount of fuel introduced into the combustion
chamber by fuel injector 23 and the operation of valves 21, 22, 24
and 26. The temperature in the combustion chamber is preferably
maintained at a level between 1400.degree. K. and 1800.degree. K.
in order to avoid producing NO.sub.X, carbon monoxide and/or other
pollutants.
By changing the amount of air compressed by the compressor, the
amount of fuel burned varies and the work output is controlled
without changing the air-to-fuel ratio, the temperature in the
combustion chamber, or the pressure in the combustion chamber. The
temperature in the combustion chamber is set by the
computer-controlled fuel injection, the pressure is maintained by
the computer-controlled valve settings, and the air intake is
controlled by the computer to match load conditions.
When more power is desired, intake valve 21 is opened longer to let
more air into compression cylinder 11, and outlet valve 22 is
opened sooner because with more air in the cylinder, the desired
compression ratio occurs at an earlier point in the upstroke of
compression piston 14. More fuel is injected into combustion
chamber 13 so that the temperature of the gas in that chamber
remains unchanged even as more gas is delivered to it. Inlet valve
24 stays open a little longer so that the increased amount of gas
can enter expansion cylinder 12, and the opening of exhaust valve
26 is advanced so that it opens when the pressure above expansion
piston 16 approaches atmospheric pressure on its upstroke.
Temperature sensors 96 monitor the temperature in the combustion
chamber, and computer 98 adjusts the amount of fuel delivered to
that chamber to maintain the temperature in it substantially
constant at a predetermined level throughout the operating range of
the engine.
Sensor 97 monitors the pressure in the combustion chamber, and
computer 98 adjusts the timing of intake valve 21 and outlet valve
22, as well as inlet valve 20 and exhaust valve 26, to maintain the
pressure in the combustion chamber at a substantially constant
level.
Decreases in power are produced by opening intake valve 21 for a
shorter period of time to reduce the amount of air let into
compression cylinder 11, and the opening of outlet valve 22 is
delayed to maintain the desired effective compression ratio with
less air in the cylinder. The amount of fuel injected into
combustion chamber 13 is decreased so that the temperature of the
gas in that chamber remains unchanged even though less gas is being
delivered to it. Inlet valve 24 closes sooner with less gas
entering expansion cylinder 12, and the opening of exhaust valve 26
is delayed since the negative pressure above expansion piston 16
will approach atmospheric pressure at a later point in its
upstroke. Here again, the temperature and pressure in the
combustion chamber are monitored, and the amount of fuel injected
and the timing of inlet valve 24 are adjusted to maintain the
temperature and pressure at the desired levels.
With the combustion chamber running at the same temperature under
different load conditions, there is no need to use a segmented
combustion chamber or multiple fuel injectors to vary the burn
temperature as in some of the other embodiments disclosed herein.
This makes the engine simpler and less expensive to build.
Also, with a constant temperature engine, response is faster
because there is no thermal inertia to overcome when rapid power
change is required. While a constant pressure engine may take
several seconds or more to go from idle to full power, a constant
temperature engine is always at full power temperature so that full
power can be realized as quickly as air can be compressed,
typically in one or two revolutions or 1/50 of a second at 3000
RPM.
Moreover, with the engine always running at the same temperature,
the exhaust gases are always at the same temperature. This makes it
easier to scavenge waste heat and further improves efficiency over
a wide range of load conditions. Except for the scavenging of the
waste heat, an engine operating at constant pressure, as disclosed
herein, would operate with the same efficiency as an engine
operating at constant temperature, and both would have the same
amount of waste heat. However, with an engine operating at constant
pressure, the temperature of the exhaust gases can vary over a wide
range, e.g. 30.degree. C. to 300.degree. C., whereas the exhaust
gases from the constant temperature engine remain at a given
temperature, e.g. 300.degree. C. while varying in volume.
Notwithstanding the variation in volume, high temperature waste
heat at a fixed temperature is much easier to scavenge than waste
heat which varies in temperature.
The exhaust gases are at a constant temperature because the
air-to-fuel ratio does not change even as the amount of air taken
in by the engine is varied with load. As a result, the amount of
oxygen in the exhaust remains substantially constant for any
particular fuel, and that makes it possible to feed the exhaust
gases back to the intake to control NO.sub.X emissions. This is
much more difficult to do with exhaust gases from a constant
pressure engine without constant temperature as they may have a
large amount or no amount of oxygen in them, depending upon the
load and the temperature of the burn. Feeding exhaust gases back is
also more difficult with Diesel engines and other conventional
engines in which power output is varied by changing the air-to-fuel
ratio and the exhaust varies in oxygen content.
At lower load conditions, less air is taken in by the engine, less
air requires less fuel to maintain the same temperature in the
combustion chamber, and because less air is being added to the
combustion chamber, the inlet valve is open for a proportionately
shorter period of time. Although the percentage of gas expansion
remains the same as with higher loads, the total work output is
reduced, with a smaller amount of pressurized gas going to the
expansion cylinder. For example, at half load, the air intake is
half of that at full load, the fuel injected into the combustion
chamber is one-half of the amount injected at full load, and
consequently the power output is only half of what it is with a
full load. With the reduced air intake, the inlet valve is open for
a smaller portion of the stroke, and in this example, it still
opens at or near top dead center, but it stays open for only about
17.5% of the expansion stroke, rather than about 25%-30%. The
expansion piston does useful work until the gas in the cylinder is
expanded and the pressure drops approximately to atmospheric
pressure, which in this example occurs when the piston has traveled
about 70% of its downward stroke. The pressure at BDC is
sub-atmospheric, and the exhaust valve does not open until the
piston is on its upstroke and the pressure is back up to or
slightly above atmospheric pressure. Opening the exhaust valve on
the upstroke has the advantage of recapturing any work done by the
piston on its downstroke when the pressure is subatmospheric.
Thus, the difference in running at partial load is that less air is
taken into the engine by adjusting the intake valve timing. The
outlet valve is adjusted to open later so that the compression
pressure is maintained with less air intake. Less fuel is needed to
heat the mixture in the combustion chamber to the same temperature
because there is less air to be heated. With a smaller amount of
air, less fuel produces the same amount of heating so that the
temperature stays constant while the amount of heated air available
to the expander is less. Less available gas for expansion reduces
the work output. The reduction in the pressurized gas available for
the expander is compensated for by opening the inlet valve for a
shorter period of time and by delaying the opening of the exhaust
valve. In this way, the efficiency of the engine is maintained
throughout the load ranges of the engine.
The power output of the engine can be boosted by the use of a turbo
charger or a super charger to boost the pressure of the incoming
air. The advantage of doing this in the engine of the invention is
that a turbo charger or super charger can increase the inlet
pressure by 50 percent and realize additional expander volume for
added power output. This can be illustrated by considering several
possible configurations of the engine. In these examples, a 2:1
volumetric expansion, or burn ratio, is assumed, but other ratios
work equally as well.
As discussed above, the burning of fuel in the engine can easily
result in a volumetric expansion of 2:1, and with a volumetric
expansion of 2:1 and venting near atmospheric pressure, the ideal
ratio of compressors to expanders is 1:2. If desired, other
volumetric expansions can, of course, be used, with the ideal ratio
of compressors to expanders being the reciprocal of the
expansion.
In a four cylinder engine having two compressors and two expanders,
there are two power strokes per revolution of the engine. With a
2:1 volumetric expansion and venting near atmospheric, one of the
two compressor cylinders could supply all of the gas required by
the expanders during normal operation of the engine, with the
second helping to compensate for decreased airflow due to altitude,
high ambient temperatures, or short cycle time (high RPM).
In a six cylinder engine having two compressors and four expanders,
with a volumetric expansion of 2:1, the two compressor cylinders
are fully utilized, and there are four power strokes per revolution
of the engine.
FIG. 13 illustrates an eight cylinder engine having two
compressors, six expanders, and a turbo charger for boosting the
intake pressure to the compressors. With a volumetric expansion of
1:2 and without the turbo charger, the two compressor cylinders
would not have enough capacity to adequately supply the six
expanders at full load. With the turbo charger providing a low
pressure boost to increase the intake pressure to the compressors
from atmospheric pressure to about 1.5 atmospheres, the two
compressors will supply as much air as three compressors receiving
air at atmospheric pressure. Thus, the two compressor cylinders are
able to fully supply the six expander cylinders with pressurized
gas after the volume of the gas is doubled in the combustion
chamber.
With the engine of the invention, low-pressure boost can be
utilized with any cylinder configuration and/or expansion ratio. It
is not limited to cylinders of equal size or to the ratios given in
the foregoing examples.
In the constant temperature engine, where the power output is
proportional to the amount of air passing through the engine, the
boost is most effective at high power levels, and for even higher
power levels a higher boot can be used. If a 14.7 psi boost is
used, for example, the eight cylinder engine will take in the same
amount of air per revolution as a standard eight cylinder engine
since two cylinders taking in air at 2 atmospheres is equivalent to
four standard cylinders taking in air at atmospheric pressure.
However, the engine of the invention will have six power strokes
per revolution instead of only four as in a conventional
engine.
With higher boost, the engine efficiency may be somewhat less than
with a lower boost because the expanded gas in the expansion
cylinders will have an exhaust pressure higher than when a smaller
boost is used. Thus, some work of expansion will be lost. However,
this loss is not very large compared to the significantly increase
in the maximum power of the engine.
In all of the disclosed embodiments, with combustion occurring in a
separate combustion chamber, the engine can run leaner than engines
where combustion takes place in the same cylinders where
compression and expansion occur, and running lean generates more
heat per unit of fuel and thus provides higher efficiency. Engines
in which combustion occurs in cylinders with pistons are limited in
their ability to use leaner mixtures because of the possibility of
the leaner mixture burning holes in the pistons.
The engine has unusually low heat loss, which further improves
efficiency. Pressurized gas can be expanded to its useable limit
near atmospheric pressure. Discharging the exhaust gases at
atmospheric pressure reduces the temperature of the exhaust and,
hence, the amount of heat which is lost with them. Moreover, the
head of the engine can be relatively small, with relatively little
surface area to lose heat to the ambient air. Also, in an engine
which does not require water cooling of the head, there is less
heat loss than in engines which are cooled.
The engine produces substantially no NO.sub.X, unburned
hydrocarbons or carbon monoxide, and emits only minimal particulate
matter, smoke and soot, and it does so without additional
components such as catalytic converters and particle filters.
In conventional gas and Diesel engines, NO.sub.X is produced when
the flame temperature exceeds 1800.degree. K., and it is commonly
reduced by monitoring the exhaust and redirecting the exhaust back
to the air intake if it is rich in oxygen. With Diesel engines,
some form of after treatment with a reducing agent such as urea may
also be required.
In the engine of the invention, the temperature in the combustion
chamber is monitored and controlled to limit the maximum burn
temperature to 1800.degree. K., which is below the range where
NO.sub.X is formed. Although the engine temperature can be set to
different values for specific needs, the engine is intended to
operate at a constant temperature over a wide range of loads and
speeds. Since the engine does not have widely varying temperature
swings like other engines, temperature control is much easier to
maintain and NO.sub.X pollution is much easier to avoid.
Unburned hydrocarbons may occur in some engines because the time
the fuel remains in the cylinders is too short for complete
combustion, and some of the fuel is left in the cylinders without
being burned. In a typical engine running at 3,000 RPM, for
example, the fuel must be mixed, ignited and burned and exhaust
must start in only 1/100 of a second. In addition, the water cooled
cylinders in such engines can be cold enough to quench the flame
front of the burning fuel, which can further prevent all of the
fuel from burning. The unburned fuel condenses on the cylinder
walls and is then blown out with the exhaust.
The engine of the invention does not produce significant amounts of
unburned hydrocarbons. The burning takes place in a thermally
insulated combustion chamber which has hot walls that do not quench
the flame front and do not cause condensation of the fuel. The
combustion chamber operates at high pressure and contains a much
larger volume of compressed air than a standard engine. As a
result, the gases remain in the combustion much longer than they do
in the cylinders of conventional engines, and thus there is more
time to complete the burn. The burn time in an engine of the
invention is typically 2 to 100 times the burn time in conventional
engines. If there is any pollution in the exhaust, it is usually a
result of the residence time for the burning gas in the combustion
chamber not being long enough, and thus it can be eliminated by
increasing the volume of the combustion chamber.
In addition, the combustion chamber produces turbulence which
causes more complete mixing and further reduces the chance of
having any unburned hydrocarbons. The sharp protrusions that form
hot spots in the combustion chamber also create turbulence and help
to ensure complete combustion and prevent unburned hydrocarbons
from leaving the combustion chamber as pollutants.
Carbon monoxide (CO) is produced in other engines when there is not
enough time for complete combustion of the fuel, and/or when the
flame temperature is too low for oxygen in the air to combine with
CO to produce harmless carbon dioxide (CO.sub.2), and/or when there
is not enough oxygen to combine with the CO to make CO.sub.2.
As discussed above, with the engine of the invention, the fuel
remains in the combustion chamber much longer than it does in
conventional engines. CO emissions are significantly reduced or
eliminated, because there is much more time to complete the burn
process. In addition, in embodiments where the burn temperature is
maintained at a substantially constant temperature and power output
is set by controlling the amount of air entering the engine, the
burn temperature is monitored and controlled so that it is always
above the 1400.degree. K. required to prevent the production of CO
regardless of load. CO production is further prevented by running
the engine with leaner fuel mixtures than are possible in other
engines. The leaner mixtures have an abundance of oxygen which can
combine with CO to convert it to CO.sub.2. With the abundance of
oxygen and by operating at the correct temperature for extended
periods of time, the engine can avoid producing measurable amounts
of CO.
Soot and other particulate matter are typically produced by the
high pressures that are present in very high compression ratio
engines by injecting fuel into air that is too hot and by burning
rich fuel mixtures. With the engine of the invention, however, the
long residence time of the fuel in the combustion chamber is
effective in burning up particulate matter and soot and thereby
converting it from a carbon rich material to water vapor and
CO.sub.2. In addition, in some embodiments, the engine operates
most efficiently with compression ratios between 10:1 and 15:1
where the potential for making soot is substantially less than in
Diesel engines which operate at significantly higher compression
ratios. Soot production is further reduced by maintaining the
temperature of the air at the point of injection below the
temperature at which soot is produced. Thus, for example, with the
engine having a compression ratio of 13:1, the temperature of the
compressed air is about 850.degree. K., which is below the critical
fuel injection temperature for soot production (900.degree. K.) and
also well below the injection temperatures of Diesel engines which
are typically about 1200.degree. K. Also, with the lean fuel
mixtures on which the engine can operate, there is an abundance of
oxygen to complete the burning process and convert all of the soot
into water vapor and harmless carbon dioxide.
With the longer burn time and no cool spots to quench the flame,
the engine of the invention provides nearly complete combustion
without after treatment such as a catalytic converter or filter.
FIG. 14 illustrates the low levels of pollutants produced by the
engine of the invention without after treatment in comparison with
the pollutants produced by other modern engines after treatment by
a catalytic converter. The pollutants shown in this graph are CO,
NO.sub.X, opacity (a measure of soot and smoke), and hydrocarbons,
with the amounts of CO, NO.sub.X, and hydrocarbons being shown in
parts per thousand (ppt) and the opacity being shown as a
percentage. The engines include three turbo charged diesels TD-1,
TD-2, TD-3 and one turbo charged gasoline engine T-Gas in addition
to the engine of the invention.
As can be seen from FIG. 14, the CO produced by the three tubo
diesel engines ranges from about 0.2 to 1.6 ppt, and the CO
produced by the turbo charged gas engine is approximately 1.4 ppt.
In contrast, the CO produced by the engine of the invention is
close to zero. The NO.sub.X produced by the turbo diesel and turbo
gas engines ranges from less than 0.1 ppt to almost 0.3 ppt for the
diesels and is almost 2.0 ppt for the gas engine. The opacity of
the exhaust from the three turbo diesels ranges from about 1.0
percent to more than 3.2 percent, and the opacity of the exhaust
from the turbo gas engine almost 0.4 percent. The hydrocarbons
produced by the diesels range from zero ppt to more than 1.2 ppt,
and the hydrocarbons produced by the gas engine are about 0.4 ppt.
In contrast, the engine of the invention produces almost no
NO.sub.X and no hydrocarbons, and the opacity of the exhaust from
that engine is essentially zero.
Although other engines can produce low pollution for some
pollutants they cannot provide low pollution for all pollutants
simultaneously even when using expansive catalytic converters. The
engine of the invention can provide virtually zero pollution for
all the mentioned pollutants simultaneously even without the aid of
catalytic converters or other after treatment.
Temperature plays a very important part of pollution control in
today's engines. As discussed above, low temperatures can cause
incomplete combustion and the formation of CO, and high
temperatures can cause the production of NO.sub.X. Conventional
engines attempt to reduce the maximum temperature by reducing the
oxygen in the cylinder, recirculating exhaust gases, altering
ignition and/or fuel injection, and reducing the compression
ratio.
The constant pressure engine of the invention can maintain burn
temperatures within the range of 1400.degree. K. to 1800.degree. K.
by using a segmented combustion chamber and bypasses so that a
controlled portion of the gas is passes through the area where the
burn is taking place. With its computer controlled fuel injection
and valves, the constant temperature engine can easily provide a
desired temperature in the 1400.degree. K. to 1800.degree. K. range
without a segmented chamber or bypassing.
The very low pollution levels in the exhaust from the engine of the
invention have caused speculation as to the mechanism that controls
NO.sub.X production and recombination. It now appears that it may
be possible to operate at temperatures above 1800.degree. K., e.g.
2000.degree. K. or more, without the production of NO.sub.X because
of the long burn time provided by the engine. Although the exact
mechanism is not known, it is believed that the NO.sub.X molecule
may not be stable at higher temperatures and that it dissociates
into its components which recombine to form O2 and N2, which are
more stable. In conventional engines, the NO.sub.X pollutants are
cooled rapidly and the NO.sub.X molecule is frozen as NO.sub.X
before it can dissociate into oxygen and nitrogen which recombine
into harmless O.sub.2 and N.sub.2.
In the constant temperature engine, other operating parameters can
also remain constant. This is a significant advantage because It is
easier to maintain high performance, prevent pollution, and
maintain high efficiency if parameters such as the air to fuel
ratio, spark advance, and compression ratio are not constantly
changing with load, engine speed, and driving conditions. Table 1
lists engine parameters that are desirable to have constant and
shows which of those parameters are constant with different engine
designs. In this table "Const P" designates a constant pressure
engine, and "Const T/P" designates the constant temperature,
constant pressure engine of the invention.
TABLE-US-00001 TABLE 1 Engine Parameters Diesel Otto Const P Const
T/P Compression Ratio Constant Variable Constant Constant Air Fuel
Ratio Variable Constant Variable Constant Burn Temperature Variable
Variable Variable Constant Burn Pressure Variable Variable Constant
Constant Exhaust Pressure Variable Variable Constant Constant
Exhaust Temperature Variable Variable Variable Constant Torque
700-4000 RPM Variable Variable Constant Constant Air Intake to HP
Ratio Variable Variable Variable Constant Efficiency at Large
Variable Variable Constant Constant and Small Loads Percent of
Oxygen Variable Constant Variable Constant in Exhaust
In general, the more of these parameters are constant, the easier
it is to provide pollution-free, high efficiency over all engine
loads and speeds. As can be seen from the table, in a diesel engine
only the compression ratio remains constant, and in an Otto cycle
engine only the air-to-fuel ratio and the percentage of oxygen in
the exhaust remain constant. In the constant pressure engine of the
invention, the compression ratio, burn pressure, exhaust pressure,
torque, and efficiency at large and small loads remain constant,
and in an engine in which the temperature and pressure are both
constant, the compression ratio, fuel-to-air ratio, burn
temperature, burn pressure, exhaust pressure, exhaust temperature,
torque, air intake to horse power ratio, efficiency at large and
small loads, and percentage of oxygen in the exhaust all remain
constant.
Although it is useful to have all four of the valves (intake,
outlet, inlet, and exhaust) be variable in a constant pressure
engine, a constant pressure engine can be run with only the inlet
and outlet valves being variable. However, in a constant pressure,
constant temperature engine in which air flow through the engine is
varied to control power output, the engine runs most efficiently
when the intake, outlet, inlet, and exhaust valves are all
variable. The constant temperature engine can also run with two or
more of valves of fixed timing, but efficiency would be compromised
at some loads.
The invention has a number of important features and advantages.
With widely variable valve timing, complete burning of fuel at all
engine speeds and loads, and the ability to vary the amount of air
intake and exhaust pressures without doing any net work against
atomospheric pressure, the invention provides a highly flexible
engine which can operate with high efficiency at substantially all
engine speeds and load conditions.
By separating the compression, combustion, and expansion phases of
the cycle, better control of each is obtained, and efficiency is
improved by exhausting the spent gases from the expansion cylinder
at or near atmospheric pressure, where the energy remaining in them
due to pressure is negligible. This results in a significant
improvement over other engines where as much as 30 percent of the
total engine power is wasted through the exhaust. As the pressure
of the exhaust gases is reduced, so is the temperature of the gas
being expanded, and lower exhaust temperatures also provide higher
engine efficiency.
With the variable valves, the compression ratio of the compression
cylinders and the expansion ratio of the expansion cylinders can be
adjusted by controlling the amount of air taken into the
compression cylinders and the amount of gas delivered to the
expansion cylinders. In addition, the expansion ratio can be made
higher than in the compression ratio, which is not possible in
other engines.
The invention also avoids the loss of power and efficiency which
occurs in other engines when the pressure in the cylinders drops
below atmospheric pressure and the engine must do work against the
atmospheric pressure on the under sides of the pistons. By
controlling the valve timing so that no valve in the compressor or
expander is opened on the upstroke of a piston until the pressure
in the cylinder is no longer subatmospheric, the work done against
atmospheric pressure is stored and then recaptured so the net
effect on the efficiency of the engine for having done work against
atmospheric pressure is essentially zero.
With no valves extending into the cylinders, the volumes of both
the compression cylinders and the expansion cylinders can go almost
to zero when the pistons are at their top dead center positions,
and volumetric efficiency is, thus, maximized which further adds to
fuel efficiency.
Moreover, the engine does not have the problem of decreased
efficiency which other engines may experience when the amount of
air admitted on the intake stroke is reduced at power levels less
than full power. The problem arises in other engines because
reducing the air intake causes the pressure in the cylinder to drop
below atmospheric pressure during the downward stroke of the
piston. This reduced amount of air reduces the effective
compression ratio and, thus, the efficiency of the engine and
causes the piston to do lost work against the atmospheric pressure
on the underside of the piston. The engine of the invention,
however, does not have that problem because the top dead center
pressure of the compression cylinder is determined by when the
outlet valve opens to admit the compressed air to the combustion
chamber and when the inlet valve closes, which determines how much
air is admitted to the compression cylinder. Since the volume of
the compression cylinder goes almost to zero, the compression
pressure can be set to almost any desired level regardless of how
much air was admitted to the cylinder. Thus, constant efficiency
can be provided at varied air intake levels.
Another advantage of the invention is that the engine can run with
a substantially constant compression ratio under substantially all
load conditions, whereas in other engines the compression ratio can
vary with load by as much as a factor of 3. Since the efficiency of
an internal combustion engine is proportional to the compression
ratio (at least for ratios up to about 20:1), with the
substantially constant compression ratio, the efficiency of the
engine remains high throughout its range of operation.
Moreover, with the compression ratio substantially constant and the
exhaust pressure effectively equal to atmospheric pressure at all
loads and speeds, the torque of the engine is also substantially
constant for all loads and engine speeds. Furthermore, with
combustion not taking place in a cooled chamber with moving
pistons, the engine does not have limitations on speed and torque
that other engines typically have. There is no piston to outrun the
flame front and no possibility of valve float. This allows the
engine to run very efficiently at all speeds and loads.
The flat torque curve has another advantage in that it allows the
engine to be used with a transmission which has fewer gears and is
therefore smaller, less expensive, and lighter in weight than the
transmissions required by other engines. This reduction in weight
further increases fuel efficiency.
Since the fuel is fully burned in a separate combustion chamber,
full power is applied to the expansion pistons when they are at top
dead center. Therefore, the expanding gases push on the pistons for
more of their stroke than in other engines where the flame front
moves slowly and does not produce maximum pressure until the flame
front reaches the cylinder walls and the pistons have moved well
past top dead center, e.g. 45 degrees past top dead center in an
engine running at 3,000 RPM. Thus, the maximum pressure is
available longer and the total work output is greater for a given
amount of hot gas. This also results in higher fuel efficiency than
is possible in other engines.
The engine provides a significant improvement in fuel efficiency,
and with closed loop pressure and temperature controls and no
combustion in the cylinders with moving pistons, it produces
substantially no NO.sub.X, unburned hydrocarbons or CO, and emits
minimal particulate matter such as smoke or soot. Since the engine
runs so cleanly and quietly, in many applications it may not
require either a catalytic converter or a muffler. The engine can
run on different fuels, and can make necessary adjustments
automatically as different fuels are supplied.
In some embodiments, the engine provides variable engine braking as
well as very efficient and effective compression release engine
braking which is also much quieter than such braking with
conventional Diesel engines. Unlike other internal combustion
engines, the engine of the invention is capable of operating at
high efficiency even at partial loads. The engine is easy to start
and does not need a dedicated starting motor. It requires no spark
plugs or ignition system, and maintenance requirements are low.
The ratio of compression cylinders to expansion cylinders is not
fixed, and the cylinders can also have similar or different bores
and/or strokes. For example, a 4-cylinder engine may have two
compression cylinders and two expansion cylinders. A 6-cylinder
engine may have two compression cylinders and four expansion
cylinders or an equal number of each. Similarly, different
embodiments of the engine can have different numbers of combustion
chambers.
Moreover, with the invention, the horsepower of a given engine can
be greatly increased for a short period of time without appreciably
affecting the overall efficiency of the engine. Thus, by
sacrificing efficiency for a just few seconds at a time, horsepower
can be increased by 50% or more, when needed, such as when
accelerating a vehicle onto a freeway.
In the embodiments in which temperature is maintained substantially
constant and power is varied by controlling amount of air passing
through the engine, there is substantially no chance of producing
pollution as a result of having the engine running too hot or too
cool, and the engine also has many of the same advantages as the
other embodiments disclosed herein. It can, for example, start at
low compression ratios, e.g. 3:1 or 4:1, and generally does not
require a dedicated starting motor. It can idle at a speed of about
50 RPM, and has a substantially flat torque curve. It can burn a
variety of fuels without producing NO.sub.X, CO, unburned
hydrocarbons, or soot, and it permits good volumetric efficiency by
allowing the volumes in the cylinders go almost to zero with the
pistons in their top dead center positions.
As in the other embodiments, the valving and intake manifold can be
utilized to provide quiet compression release engine braking. The
engine can have different combinations of piston diameters and
strokes and different numbers of compression and expansion pistons.
It also has the ability to increase air intake when air density is
low due to atmospheric conditions, high altitude, or high ambient
temperatures, and power boosts can be provided by increasing air
intake to an amount greater than that which can be expanded to
atmospheric pressure.
Although the temperature can remain constant over a wide range of
engine speeds and loads, the temperature chosen can be varied for
different considerations such as extending part life or to provide
the fastest response to power increases. As a result, the engine
can be referred to as an adjustable constant temperature engine,
and somewhat surprisingly, the pressure may also stay virtually
constant in this constant temperature engine. Work output and fuel
consumption are controlled by controlling the amount of air
compressed by the compressor. Efficiency is not lost as it is in
other engines that restrict air flow because the engine recovers
work that is done at reduced pressure and because the engine
maintains the same high efficiency and effective compression ratio
at all loads, speeds, and conditions.
With the intake, outlet, inlet, and exhaust valves all being
variable and under computer control, the engine can be operated in
a constant pressure mode, a constant temperature mode, or a
constant pressure and constant temperature mode with just a change
in software.
It is apparent from the foregoing that a new and improved internal
combustion engine and method have been provided. While only certain
presently preferred embodiments have been described in detail, as
will be apparent to those familiar with the art, certain changes
and modifications can be made without departing from the scope of
the invention as defined by the following claims.
* * * * *
References